Disclosed herein are methods for preparing phase change inks. More specifically, disclosed herein are methods for preparing phase change inks containing an ink carrier and a pigment colorant. One embodiment is directed to a process for preparing a phase change ink composition which comprises (a) a phase change ink carrier, said carrier comprising at least one nonpolar component and at least one polar component, and (b) pigment particles, said process comprising (1) selecting at least one of the polar carrier components to be a pigment particle dispersant; (2) admixing the pigment particles with the dispersant; (3) extruding the mixture of pigment particles and dispersant in an extruder at a temperature that is at or above about the peak crystallization temperature of the dispersant and below about the peak melting temperature of the dispersant, thereby forming a pigment dispersion; (4) subsequent to extrusion of the pigment dispersion, adding to the pigment dispersion any remaining polar components and the nonpolar component; and (5) subjecting the resulting mixture of pigment dispersion, polar component, and nonpolar component to high shear mixing to form an ink.
In general, phase change inks (sometimes referred to as “hot melt inks”) are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks have also been used in other printing technologies, such as gravure printing, as disclosed in, for example, U.S. Pat. No. 5,496,879 and German Patent Publications DE 4205636AL and DE 4205713AL, the disclosures of each of which are totally incorporated herein by reference.
Phase change inks for color printing typically comprise a phase change ink carrier composition which is combined with a phase change ink compatible colorant. In a specific embodiment, a series of colored phase change inks can be formed by combining ink carrier compositions with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes, namely, cyan, magenta, yellow and black, although the inks are not limited to these four colors. These subtractive primary colored inks can be formed by using a single dye or a mixture of dyes. For example, magenta can be obtained by using a mixture of Solvent Red Dyes or a composite black can be obtained by mixing several dyes. U.S. Pat. No. 4,889,560, U.S. Pat. No. 4,889,761, and U.S. Pat. No. 5,372,852, the disclosures of each of which are totally incorporated herein by reference, teach that the subtractive primary colorants employed can comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and Basic Dyes. The colorants can also include pigments, as disclosed in, for example, U.S. Pat. No. 5,221,335, the disclosure of which is totally incorporated herein by reference. U.S. Pat. No. 5,621,022, the disclosure of which is totally incorporated herein by reference, discloses the use of a specific class of polymeric dyes in phase change ink compositions.
Phase change inks have also been used for applications such as postal marking and industrial marking and labelling.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Compositions suitable for use as phase change ink carrier compositions are known. Some representative examples of references disclosing such materials include U.S. Pat. No. 3,653,932, U.S. Pat. No. 4,390,369, U.S. Pat. No. 4,484,948, U.S. Pat. No. 4,684,956, U.S. Pat. No. 4,851,045, U.S. Pat. No. 4,889,560, U.S. Pat. No. 5,006,170, U.S. Pat. No. 5,151,120, U.S. Pat. No. 5,372,852, U.S. Pat. No. 5,496,879, European Patent Publication 0187352, European Patent Publication 0206286, German Patent Publication DE 4205636AL, German Patent Publication DE 4205713AL, and PCT Patent Application WO 94/04619, the disclosures of each of which are totally incorporated herein by reference. Suitable carrier materials can include paraffins, microcrystalline waxes, polyethylene waxes, ester waxes, fatty acids and other waxy materials, fatty amide containing materials, sulfonamide materials, resinous materials made from different natural sources (tall oil rosins and rosin esters, for example), and many synthetic resins, oligomers, polymers, and copolymers.
U.S. Pat. No. 4,889,560 (Jaeger et al.), the disclosure of which is totally incorporated herein by reference, discloses a phase change ink carrier composition combined with a compatible colorant to form a phase change ink composition. A thin film of substantially uniform thickness of that phase change ink carrier composition, and the ink produced therefrom, has a high degree of lightness and chroma. The thin films of a substantially uniform thickness of the ink composition are also rectilinearly light transmissive. The carrier composition is preferably a fatty amide-containing compound.
U.S. Pat. No. 4,889,761 (Titterington et al.), the disclosure of which is totally incorporated herein by reference, discloses a method for producing a light-transmissive phase change ink printed substrate is described which comprises providing a substrate, and then printing on at least one surface of the substrate a predetermined pattern of a light-transmissive phase change ink which initially transmits light in a non-rectilinear path. The pattern of solidified phase change ink is then reoriented to form an ink layer of substantially uniform thickness. This ink layer will, in turn, produce an image which then will transmit light in a substantially rectilinear path. In one aspect of the invention, the substrate is light transmissive, and the reoriented printed substrate exhibits a high degree of lightness and chroma, and transmits light in a substantially rectilinear path. In this way, the reoriented printed substrate can be used in a projection device to project an image containing clear, saturated colors.
U.S. Pat. No. 5,372,852 (Titterington et al.), the disclosure of which is totally incorporated herein by reference, discloses a phase change ink composition that is indirectly applied to a substrate by raising the temperature of the phase change ink composition to form a liquid phase change ink composition, applying droplets of the phase change ink composition in a liquid phase to a liquid intermediate transfer surface on a solid support in a pattern using a device such as an ink jet printhead, solidifying the phase change ink composition on the liquid intermediate transfer surface, transferring the phase change ink composition from the liquid intermediate transfer surface to the substrate, and fixing the phase change ink composition to the substrate. The phase change ink composition is malleable when the ink is transferred from the intermediate transfer surface to the substrate and is ductile after the ink has been transferred to the substrate and cooled to ambient temperature to preclude the ink from crumbling and cracking.
U.S. Pat. No. 5,621,022 (Jaeger et al.), the disclosure of which is totally incorporated herein by reference, discloses a phase change ink composition wherein the ink composition utilizes polymeric dyes in combination with a selected phase change ink carrier composition.
U.S. Pat. No. 5,782,966 (Bui et al.), the disclosure of which is totally incorporated herein by reference, discloses resins and waxes made by reacting selected nucleophiles, including alcohols and/or amines, with an isocyanate. The order of addition of the isocyanate and the different nucleophiles can tailor the distribution of di-urethane, mixed urethane/urea, and/or di-urea molecules in the final resin product. The isocyanate-derived resin and wax materials are useful as ingredients as phase change ink carrier compositions used to make phase change ink jet inks.
U.S. Pat. No. 5,902,841 (Jaeger et al.), the disclosure of which is totally incorporated herein by reference, discloses a phase change ink composition wherein the ink composition utilizes colorant in combination with a selected phase change ink carrier composition containing at least one hydroxy-functional fatty amide compound.
U.S. Pat. No. 5,994,453 (Banning et al.), the disclosure of which is totally incorporated herein by reference, discloses phase change carrier compositions made from the combination of at least one urethane resin; at least one urethane/urea resin; at least one mono-amide; and at least one polyethylene wax. The order of addition of the reactants to form the reactant product urethane resin and urethane/urea resin permits the tailoring or design engineering of desired properties.
U.S. Pat. No. 6,174,937 (Banning et al.), the disclosure of which is totally incorporated herein by reference, discloses a phase change ink comprising a material of the formula
wherein X1, X2, X3, and X4 are segments comprising atoms selected from groups V and VI of the periodic table; wherein at least one R1 and R5 comprises at least 37 carbon units; and wherein R2, R3, and R4 each comprise at least one carbon unit. The invention further encompasses a composition of matter, as well as methods of reducing coefficients of friction of phase change ink formulations.
U.S. Pat. No. 6,309,453 (Banning et al.), the disclosure of which is totally incorporated herein by reference, discloses colorless compounds having a central core and at least two arms extending from the core. The core can comprise one or more atoms. The at least two arms have the formula
In such formula, Z is a segment of one or more atoms; j is an integer from 1 to about 300 and can be different at one of the at least two arms than at another of the at least two arms; Q is an alkyl or aryl group and can vary amongst different alkyl and aryl groups within the colorless compound; and n is an integer greater than 1 and can be different at one of the at least two arms than at another of the at least two arms. In other aspects, the invention encompasses phase change inks incorporating the above-described colorless compound as toughening agent, and methods of printing with such phase change inks. The invention further includes a solid ink comprising a colorant and a colorless compound of the formula
In such formula, X is a single atom corresponding to N or O; Z1 and Z2 are substituents comprising one or more atoms, and can be the same as one another or different from one another; and j is an integer from 1 to about 50.
U.S. Pat. No. 6,380,423 (Banning et al.), the disclosure of which is totally incorporated herein by reference, discloses colorless compounds having a central core and at least two arms extending from the core. The core can comprise one or more atoms. The at least two arms have the formula
In such formula, Z is a segment of one or more atoms; j is an integer from 1 to about 300 and can be different at one of the at least two arms than at another of the at least two arms; Q is an alkyl or aryl group and can vary amongst different alkyl and aryl groups within the colorless compound; and n is an integer greater than 1 and can be different at one of the at least two arms than at another of the at least two arms. In other aspects, the invention encompasses phase change inks incorporating the above-described colorless compound as toughening agent, and methods of printing with such phase change inks. The invention further includes a solid ink comprising a colorant and a colorless compound of the formula
In such formula, X is a single atom corresponding to N or O; Z1 and Z2 are substituents comprising one or more atoms, and can be the same as one another or different from one another; and j is an integer from 1 to about 50.
U.S. Pat. No. 5,221,335 (Williams et al.), the disclosure of which is totally incorporated herein by reference, discloses a stabilized pigmented hot melt ink containing a thermoplastic vehicle, a coloring pigment, and a dispersion-stabilizing agent to inhibit settling or agglomeration of the pigment when the ink is molten, comprising 1.5 to 20 weight percent of a nitrogen-modified acrylate polymer. A preferred dispersion-stabilizing agent is the nitrogen-modified methacrylate polymer marketed by Rohm and Haas as Plexol 1525.
U.S. Pat. No. 5,800,600 (Lima-Marquez et al.), the disclosure of which is totally incorporated herein by reference, discloses a solid ink jet ink composition which is suitable for hot melt applications having a carrier having an electrical resistivity of at least 108 Ohm.cm, insoluble marking particles, and a particle charging agent dispersed in it. The marking particle may be a pigment, an insoluble dyestuff, a polymer, or mixture thereof. The particle charging agent may be a metal soap, a fatty acid, lecithin, an organic phosphorous compound, a succinimide, a sulfosuccinate, petroleum sulfonates, a soluble or partially soluble resin such as a modified rosin ester, an acrylic, a vinyl, a hydrocarbon, or a mixture thereof. The solid ink jet ink composition may further include a viscosity controller. The ink may be capable of being heated to 155° C. and have at that temperature a viscosity of between 5 to 150 centipoise.
While known compositions and processes are suitable for their intended purposes, a need remains for improved phase change inks. In addition, a need remains for phase change inks having pigment colorants. Further, a need remains for phase change inks having pigment colorants wherein the pigment particles are stable and uniformly dispersed within the ink formulation. Additionally, a need remains for ink sets of different colored inks wherein some inks have pigment colorants and some inks have dye colorants, and wherein the other ink components remain the same for both the pigment-based inks and the dye-based inks. There is also a need for phase change inks containing pigment colorants that have increased stability and lightfastness at elevated temperatures, thereby enabling improved fade resistance upon exposure to heat and/or light. In addition, there is a need for phase change inks containing pigment colorants that exhibit reduced diffusion of the colorant from the ink to paper, thereby enabling reduced showthrough. Further, there is a need for phase change inks containing pigment colorants that exhibit reduced diffusion of colorants from image areas of one color to image areas of another color, thereby enabling improved image quality. Additionally, there is a need for phase change inks containing pigment colorants wherein the pigment colorants exhibit reduced agglomeration and settling in the ink when the ink is exposed to prolonged and/or excessive heating conditions, such as the temperatures (typically at least about 110° C., and frequently at least about 135° C.) and time periods (typically at least a day, and frequently at least a week) to which phase change inks are exposed in phase change ink jet printers. A need also remains for phase change inks containing pigment colorants that exhibit reduced clogging of jets in the printhead and reduced printhead failure that might be caused by agglomeration of the pigment colorant in the ink. In addition, a need remains for methods for preparing phase change inks containing pigment colorants wherein relatively high viscosity formulations can be processed effectively under high shear conditions.